Grazer behaviour can regulate large-scale patterning of community states

Ecosystem patterning can arise from environmental heterogeneity, biological feedbacks that produce multiple persistent ecological states, or their interaction. One source of feedbacks is density-dependent changes in behaviour that regulate species interactions. By fitting state-space models to large-scale (similar to 500 km) surveys on temperate rocky reefs, we find that behavioural feedbacks best explain why kelp and urchin barrens form either reef-wide patches or local mosaics. Best-supported models in California include feedbacks where starvation intensifies grazing across entire reefs create reef-scale, alternatively stable kelp- and urchin-dominated states (32% of reefs). Best-fitting models in New Zealand include the feedback of urchins avoiding dense kelp stands that can increase abrasion and predation risk, which drives a transition from shallower urchin-dominated to deeper kelp-dominated zones, with patchiness at 3-8 m depths with intermediate wave stress. Connecting locally studied processes with region-wide data, we highlight how behaviour can explain community patterning and why some systems exhibit community-wide alternative stable states.

Automated summary

This study found that behavioral feedback mechanisms in marine ecosystems can explain the formation of different states dominated by kelp or sea urchins in certain areas. In California, starvation intensifies grazing behavior, leading to reef-scale alternately stable states of kelp and sea urchin barrens; while in New Zealand, sea urchins avoid dense kelp stands, driving the transition from shallow urchin-dominated zones to deeper kelp-dominated zones in areas influenced by moderate wave stress at 3-8 meters depths.